(1) Field of the Invention
The present invention relates to an image forming apparatus and an image forming method, and particularly to an image forming apparatus including a fixer that fixes a toner image onto a sheet by heat and pressure.
(2) Related Art
The image forming apparatus disclosed in Japanese Patent Application Publication No. H11-54242 has been known as an image forming apparatus including a fixer that fixes a toner image onto a sheet by heat and pressure. In general, the fixer included in this type of image forming apparatus forms a nip by bringing a fixing roller and a pressure roller into pressure-contact with each other, causes a sheet to pass through the nip while heating the fixing roller by a heater or the like, and thus to fix a toner image onto the sheet. At this time, a nip width that is a width of the nip in a conveyance direction of the sheet varies due to thermal expansion of the pressure roller, and so on. Also, failure of appropriate control of the nip width to be a predetermined value might cause a problem such as crinkles, curls, and the like on the sheet. Accordingly, in order to appropriately control the nip width, the fixer included in the image forming apparatus such as described above includes a temperature adjuster such as an air blower and a heater, an automatic pressure-contact and release mechanism that changes the pressure-contact status between the fixing roller and the pressure roller in accordance with the operation status of the fixer, or the like.